1. Field of the Invention
The invention relates to a method of fabricating an active layer thin film, more particularly, to a method of fabricating an active layer thin film by a precursor solution.
2. Description of the Prior Art
At present, during the fabrication of liquid crystal displays (LCDs), thin film transistor array (TFT Array) process still uses those technologies similar to the traditional semiconductor manufacturing to form a number of transistors on a glass substrate, for example, through vacuum coating, exposure, yellow development, and etching process, etc. However, as the panel size is gradually increased, the vacuum coating will result in the problems of over high cost but lower yield, etc. In a common bottom-gate thin-film transistor structure presently used, an active layer thin film is formed by Plasma Enhanced Chemical Vapor Deposition (PECVD) to deposit amorphous Si on a gate insulator on a substrate, and then spin-coated with photoresist coating, and patterned by etching after exposure and development.
But, to simplify the process and to reduce the equipment cost, it is the most practicable method that the active layer thin film is fabricated by simply and directly coating with a precursor solution, instead of the vacuum coating. And both the material properties and the process conditions should be considered in the choice and design of a precursor for preparing a precursor solution; wherein, the material properties include, for example, band gap value, Hall mobility, crystallinity, compatibility with metal layer and insulating layer, favorable impedance, and leakage current, etc., and the process conditions include, for example, the coating property, the heat treatment temperature and retention time, etc.
Now, few semiconductor films are fabricated by solution coating, and metal-chalcogenide semiconductors may be suitable under the conditions of band gap value close to that of silicon and non-toxicity. But, in the environmental conditions of non-vacuum and process temperature lower than 300° C., it is rather difficult to fabricate a transistor active layer film having the high mobility as required by the transistor operation with the metal-chalcogenide, since even if a film can be formed under such a condition, the problems of leaving group residues or film quality defects would usually result in the losses of semiconductor properties.
US patent No. 20050158909 disclosed a conventional technology wherein an active layer thin film on a transistor is fabricated by coating with a hydrazine solution of hydrazinium-based metal-chalcogenide precursor.
US patent No. 20050009225 disclosed a conventional technology wherein an active layer thin film on a transistor is fabricated by coating with hydrazine-based metal-chalcogenide precursor dissolved in a non-toxic solvent.
Although in the conventional technologies above, the active layer thin film on a substrate is fabricated by coating with a precursor solution, the hydrazine used is toxic and has a risk of explosion. Furthermore, anhydrous hydrazine must be used in synthesis of the precursor, and it is very difficult to completely remove water content in the hydrazine, which is seldom applied in the industrial production.